When running Polymat 13.0 directly on a Linux system, launching Polymat the GUI freezes. Problem does not exist if running with VNC or virtual desktop.
Polymat 13.0 still uses Zinc GUI Tool Kit.
Zinc is pretty old and exhibits a strange behavior: the Num Lock key can freeze the GUI.
Start Polymat and try to hit Num Lock key if the GUI is frozen.
It is typical that using VNC or another virtual desktop tool modifies the behavior.
Polymat 14.5 uses wxWidgets GUI layer and does not suffer from this trouble anymore.